Aluminoborosilicate glass and method for the production of crystallite-free gradient index lenses

Abstract

The invention is directed to an aluminoborosilicate glass containing alkali metals for the production of optical components with refractive index gradients which are generated by ion exchange of monovalent metal ions in a base glass comprising at least silicon oxide, boron oxide, aluminum oxide and an alkali metal oxide, particularly for the production of gradient index lenses (GRIN lenses). The object of the invention, to find a novel possibility for producing GRIN lenses based on aluminoborosilicate glasses in which the glass has an appreciably reduced tendency toward crystallization in subsequent thermal treatment processes, is met according to the invention in an alkali-containing aluminoborosilicate glass for the production of optical components with refractive index gradients generated by ion exchange of monovalent, refractive index-changing metal ions in a base glass of SiO2, Al2O3, a metal-(III)-oxide (of B and / or Ga) and at least one metal-(I)-oxide (of Li, Na, K and / or Rb) in that defined molar ratios of metal-(III)-oxides to the metal-(I)-oxides of the base glass are adjusted within a given range in order to appreciably reduce the tendency toward crystallization of the glass for subsequent thermal treatment processes. Point defects caused by crystallites in the GRIN lenses produced in this manner are drastically reduced in this way.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority of German Application No. 103 61 555.5, filed Dec. 19, 2003, the complete disclosure of which is hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]a) Field of the Invention[0003]The invention is directed to an aluminoborosilicate glass containing alkali metals and at least a partial volume of silver ions that are introduced into a base glass of silicon oxide, boron oxide, aluminum oxide and at least one alkali metal oxide by ion exchange with alkali metal ions, particularly for gradient index lenses (GRIN lenses), and to a method for the production of GRIN lenses and other optical elements with an at least partially increased or reduced index of refraction.[0004]b) Description of the Related Art[0005]Numerous solutions are known from the prior art for producing gradient index lenses (GRIN lenses). The most effective solutions are based on borosilicate glasses which are suitable for ion excha...

AI Technical Summary

Benefits of technology

[0012]It is a primary object of the invention to find a novel possibility for producing GRIN lenses based on aluminoborosilicate glasses in which the glass has an appreciably reduced tendency toward crystallization without a deterioration of the positive characteristics known for conventional borosilicate glasses, such as meltability at temperatures conventionally used in glassmaking (up to 600° C.), with good optical quality and a high refractive index gradient and without substantial coloration after the introduction of silver.

[0049]The core idea of the invention is based on the surprisingly discovered fact that the formation of crystallization defects which occurs in particular during thermal shaping processes (e.g., rod drawing) but also during solidification from the melt and during thermal ion exchange processes can be appreciably suppressed compared to a conventional aluminoborosilicate glass (e.g., according to DD 269 615 B5) when a molar ratio of the metal-(III)-oxides to metal-(I)-oxides, as was indicated above, or at least the molar ratio between aluminum oxide and the metal-(I)-oxides of the base glass is adjusted within a given range. Particularly in the production of GRIN lenses by ion exchange (preferably Ag / Na and Li / Na), this results in advantageous optical components which achieve large differences in the index of refraction (up to Δn=0.15) with high transmission (and low coloration) in the visible and NTR spectral regions along with mechanical and chemical stability.

[0050]The invention makes it possible to realize the production of GRIN lenses based on aluminoborosilicate glasses in which the base glass, particularly in the thermal treatment steps for generating higher refractive indices and refractive index gradients, has an appreciably reduced tendency toward crystallization while retaining the positive characteristics of conventional borosilicate glasses such as meltability at temperatures conventionally used in glassmaking (up to 1600° C.) with good optical quality and a high index of refraction after the introduction of silver without substantial coloration.

Problems solved by technology

For borosilicate glasses, an unwanted coloration by silver colloids is mentioned as disadvantageous.

However, the tendency towards crystallization (nepheline) which occurs as a result of thermal shaping processes (rod drawing or float glass process) and which is noticeable as punctiform or chain defects in the GRIN lenses and generates imaging defects or scattered light is disadvantageous.

However, the addition of MgO worsens transmission and contributes to an increased tendency toward crystallization.

It cannot be determined whether or not the tendency toward crystallization is also sufficiently reduced.

All of the aforementioned references with ion exchange between silver and alkali have the common drawback that point defects which interfere with imaging systems and illumination systems occur in the finished GRIN lenses when the base glass has a significant tendency to form crystallites or has increased growth as soon as thermal treatment processes (such as thermal shaping processes, e.g., rod drawing or ion exchange processes) are applied to the glass blanks that are solidified from the glass melt.

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